Leaf spring guide for mechanical rectifier contacts



Nov. 18, 1958 o. JENSEN 2,861,154

LEAF SPRING GUIDE FOR MECHANICAL RECTIFIER CONTACTS Filed June 22, 1954 3 Sheets-Sheet 1 BY Wi Nov. 18, 1958 o. JENSEN 2,861,154

LEAF SPRING GUIDE FOR MECHANICAL RECTIFIER CONTACTS Filed June 22, 1954 I 5 Sheets-Sheet 2 ILE- 4:

EE- 5a i I 1. LL I I ll 62 J I I I l l 67 I l I l I L-- cc 1 I I 64 A 3 INVENTOR.

8 By 0770 JENSEN Nov. 18, 1958 o. JENSEN 2,851,154

LEAF SPRING GUIDE. FOR MECHANICAL RECTIFIER CONTACTS Filed June 22, 1954 5 Sheets-Sheet 3 INVENTOR. 0770 JENSEN United States Patent LEAF SPRING GUIDE FOR MECHANICAL RECTIFIER CONTACTS Otto Jensen, Malvern, Pa., assignor to I-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Application June 22, 1954, Serial No. 438,424 1 Claim. (Cl. 200-166) My invention relates to guide means for the bridging contacts of a mechanical rectifier.

The guided contact arrangement of my invention may be. applied to the type of'mechanical rectifier disclosed in co-pending application Serial No. 301,880, filed July 31, 1952; Serial No. 331,467, filed January 15, 1953, assigned to the assignee of the instant case.

A mechanical rectifier produces direct current by making bridging contact between a proper phase of an AC. system and the associated D.C. system during the time interval the particular phase of the A.-C. system is capable of delivering energy in the desired direction and breaking the bridging contact when the A.-C. phase reverses its voltage in relationship to the D.-C. voltage. This operation is performed sequentially and repeatedly in synchronism with the A.-C. frequency.

Mechanical rectifiers utilize a commutating reactor, which is a non-linear or saturable type reactor, to step the current when it passes through zero value. This operation is fully described in co-pending application Serial No. 212,017, filed February 21, 1951. During a period of each stepping operation either contact engagement or disengagement must be completed. Hence, in a three phase mechanical rectifier conversion unit it is necessary for the contact assembly to make and break the circuit 216,000 times per hour. It is therefore, apparent that the contact assembly is a vital component of the conversion unit and must be designed to contribute directly to the quality of conversion performance. C'o-pending application Serial No. 307,024, filed August 29, 1952, is directed to the contact time adjustment for the contact assembly and the instant application is directed to a guide means for the movable bridging contact.

The make and break of the contact assembly is designed to occur during the stepping length of the current so that contact engagement and disengagement will occur during zero current flow. However, even though there usually is an absence of current at the time of making and breaking connections the contact assembly must carry 5,000 amperes and serve through 1,866,000,000 operations for a 360 day period. Improper contact time adjustment for a short period of time may result in contact pitting, burning and corrosion. I

- The cooperating contacts of a mechanical rectifier may be contained in a removable and replaceable contact block in .which a helical spring is mounted for biasing the bridging contact into engaged or make position with the stationary contacts.

In the prior art arrangements, the helical spring functions as both a biasing means and a guide means. However, this arrangement has disadvantages in that during the period of contact disengagement or break the helical spring may cause the bridging movable contact to rotate about the axis perpendicular to the plane of contact and/ or move or slide in a transverse direction. These undesirable movements of the bridging contact cause creation of silver dust at the time of contact make or break. 1 My invention increases the mechanical life of the mating silver contacts by preventing the formation of silver dust. In unguided contacts silver dust is created by the minute relative motion between mating contact surfaces,

e. g. if the two mating contact surfaces are permitted to skid or slide or rotate even as little as .001" then in three months operation of the contacts the total distance traveled will be more than 30 miles and that amount ofskidding of the mating surfaces under the action of the contact spring will generate much silver dust due to abra: sions between the mating surfaces.

The silver dust is undesirable for two reasons; first it reduces the mechanical life of the contacts, and, second, the silver dust may form into a chain, one end of which might adhere to the moving contact when it openswhile the other end might rest on the stationary contact. Should this be the case, the metallic connection between the moving contact and the stationary contact will not be broken when it is supposed to be and a strong current will flow through the silver chain during the non-conducting cycle of the contacts resulting in a backfire which will shut the machine down and cause damage to the backfiring contacts as well as adjacent contacts.

Even if no actual backfire occurs due to the building up of the chain of silver dust, the individual grains of silver dust have a disturbing influence on contact life. If one silver grain is present between the moving and stationary contacts and we consider that the moving contacts are opening, then the small amount of residual current which flows through the contact on opening will flow through this single grain of silver dust. As the silver dust has a very small cross sectional area, this grain, under the influence of current flowing through it, reaches a white hot temperature and will in turn become welded to one of the mating surfaces. This process keeps on and eventually the contact surfaces will be very rough, consisting of projections on one contact and mating crevices on the other. If the projections on one contact and mating crevices on the other always match no great harm is done; but, if upon opening of the contacts a sliding motion takes place, then the projection will rub against the sides of the crevices and, therefore, prolong the contact time. This prolongation can be so severe that the contact breaks too late in the cycle and again a backfire will result.

That is, any pittings or erosion of the contacts ma occur in the form of a protrusion on one contact and a mating crevice on the other contact. If the bridging contact is rotated with respect to the stationary contact (i. e. about the longitudinal axis of the helical spring) a protrusion on one of the contacts will subsequently engage a flat portion on its cooperating contact rather than its 4 mating crevice.

Hence, the time of contact engagement will be considerably altered. That is, since the push rod which controls the movement of the movable contact travels at a speed of 27 inches per second, a one-thousandth of an inch change in the thickness of the cooperating contacts will cause an 0.8 electrical degree change in the timing.

Thus, rotation of the bridging contact, even though the contact may remain parallel and symmetrical with its cooperating stationary contacts, will result in an undesirable change in the timing operation of the mechanical rectifier. With the guide means of my instant invention, I secure a bridging contact to a fiat metal leaf spring guide to prevent rotating and sliding which thereby prevents the creating of silver dust so that the mechanical as well as the electrical life of the contact is materially improved.

The first embodiment of my invention utilizes a helical spring in connection with a leaf springwherein the helical spring serves as a biasing means and the leaf spring serves solely as a guide member. With this embodiment, the leaf spring can be relatively weak since all of 3 the biasing force is derived from the helical spring. With this embodiment the metal leaf spring is mounted at either one or two ends. I

- Another embodiment of my invention providesa relatively strong metal leaf spring which serves the dual function of biasing the bridging contact into the engaged position-and also serves as a guide means for the bridging contact, thereby eliminating the helical biasing spring.

a In mechanical rectifier installations wherein a relatively large area is provided for the contact assembly structure so that a long leaf spring can be utilized as a guide, the leaf spring of-both the embodiments will be subjected to relatively small tension stresses and hence there will bear verysmall degree'of elongationor distortion of-the'leafspring.

do this typeof installation the leaf spring will not only prevent rotation of the bridging contact, but will also prevent this unit from -sliding with respect to the stationary contact.

Accordingly, it is a primary object ofmy invention to provide a guide meansfor a bridging contact of a mechanical rectifier wherein rotation and sliding of the bridging contact member is prevented.

Another object of my invention is to provide a leaf spring arrangement which serves a dual function of biasing and guiding a moving contact of a mechanical rectifier contact assembly.

Stillanother object of my invention is to provide a guide means which will'increase the mechanical and electrical life'of the contacts by preventing the creation of silver dust.

-Still-another object of my invention is the provision of acontact assembly with a leaf spring and a helical spring in which the leaf spring serves solely as a guide -member and the helical spring serves solely as a biasing member. i

These and other objects of my invention will be apparent when taken in connection with the description ofthe drawings in which:

:Figure lis aschematic wire diagram'of a mechanical -rectifier to which my novel guided contact arrangement can be applied.

- =Figure 2 isa perspective view of the mechanical operatingmechanism and illustrates the manner in which my novel guided contacts are synchronously driven into en- .gaged and disengaged position.

'- Figure-3 is a cross sectional view of a contact assembly inwhich the bridging contact is guided by means ---of .ametal leaf spring and biased into contact engagement by means ofa helical spring. In the first embodi- .rnent of Figure 3 the guiding metal leaf spring is secured hatits opposite ends and the bridgingcontact is carried in the center thereof.

Figure 3A isa top view of the flat metal leaf spring used in the arrangement of Figure 3.

Figure 4 is a view taken in the direction of the arrows 4-4 of Figure 3.

Figure '5 isa cross sectional view of a contact assembly mounted in a mechanical rectifier unit and illustrates a-modified arrangement of the first embodiment of-Figures 3 and 4. In the modified view of Figure 5 -themetal leaf spring is secured at one end thereof, and

the bridging contact is carried by the other end thereof.

Figure 6 illustrates a second embodiment of my invention wherein the metal leaf springserves as both a guide member and a biasing member for the bridging contact. In thisembodiment the helical biasing spring is eliminated so that the leaf spring serves a dual function of both biasing and guiding the bridging contact.

Figure 6Ais a top view of the metal leaf spring which ,is used in the second embodiment of Figure 6.

In Figure 1 the source of alternating current is derived from the A.-C. voltage source which energizes the conductor 10, passes through the circuit breaker 11 to the step down transformer 12. a The current is subsequently passed through commutating reactor 13 to step the current for commutating purposes as set forth in coending application Serial No. 212,017, filed February 21, 1951. The construction of the commutating reactor is described in co-pending application Serial No. 301,880, filed July 31, 19.52. a

The current then passes through the disconnect switches 14 to the contact assemb1ies'15 and 16 which form the subject matter of the instant application. The contact assemblies 15 and 16 which sequentially is in synchrcr nism with the frequency of thesource, is connected to the alternating source buses 10a, b, and c to the direct current load buses 20 and 21.

For purposes of simplification, I have shown in Figure 2 the mechanical switching arrangement which is utilized for. phase a, it being understood that the switching apparatus for phases band c are identical in construction. This figure illustrates the manner in which my novel guide contactassembly is mechanically driven for synchronous engagement and disengagement of the contacts. 7

A synchronous motor 22 drives the shaft 23 which in turn operates the eccentric member 24 to thereby alternately. drive thepush rods 18 and 19 upwardly through the bell cranks 29. A detailed explanation of the construction of the adjustment and control means 17 is set forth in co-pending application Serial No. 307,024, filed August 29, 1952.

The upward movement of the push rod-18 will urge the disc shaped bridging contact 31 upward against the '18 and 19 will be reversed by the bell crank 29 so that the push rod 18 will be in its lowermost position and the push rod 19 will be in its uppermost position. 1 Hence, at this time the bridging contact 31 associated with the contact block assembly 15 will be in engagement with its associated stationary contacts 28 and 26 and the bridging contact associated with the contact block assembly 16 will be disengaged from its associated contacts 25 and 27.

A contact block structure 15 and 16 is similar in construction and hence for the sake of simplicity I have shown only contact block 15 in Figures 3 and 4. The contact block assembly 15 iscomprised of an insulating housing 41 which serves as a housing and support for the components thereof. A helical spring 32 is mounted therein and is lodged between the spacers 33 and 34. Bracket means 35 and 36 are secured respectively by means of the bolts and nuts 37-38, 3940 to the housing 41.

Ths housing 41 is provided with four openings 42 which extend the entire length thereof. Assembly. screws 43 are received in the longitudinal openings 42 and are in threaded engagement with internally threaded openings in the A.-C.stationary contact 28 and the D.-C. stationary contact 26. The metal leaf spring 44, to which my novel invention is specifically directed, is secured at each end by means of the rivets 45 and 46 to the bracket support members 35 and 36. The metal flat leaf spring may have a configuration similar to'that shown in Figure 3A.

' The center portion of the metal leaf spring 44 is provided with a reinforced fiat metal section 47 and v 48 which straddles thespring 44. The bridging contact S2 is sandwiched between the bridging contact 31 and the metal leaf spring 44 to insulate these members from each other.

As heretofore noted, the push rod 18 may be driven by means of a synchronous motor to thereby move the bridging contact 31 against the helical biasing spring 32 during a portion of each cycle of operation.

In the embodiment shown in Figures 3 and 4 the helical spring 32 is rigidly secured to the movable contact 31 or to the metallic guide member 44. Hence, neither rotational nor tilting motion of the helical spring 32 will be imparted to the bridging contact 31. Since the moving contact member 31 is carried by the flat leaf spring 44 the motion of this former member will be controlled and guided solely by the leaf spring 44. Since the flat leaf spring 44 is provided with stationary supports, it will not be able to rotate about an axis which is perpendicular to the plane of the bridging contact 31 and furthermore, will not have transverse motion in the plane of the bridging contact 31.

Hence, it will serve as a guide means for the moving contact 31 to prevent both rotational and sliding motion thereof. Since contact pressure between the cooperating contacts 31 and 26, 28 is derived from the heavy helical biasing spring 32 and since the leaf spring 44 does not have to impart any biasing or pressure forces on the bridging contact 31 the metal leaf spring 44 can be a relatively weak member compared to the helical biasing spring 32.

It will be noted that the ends of the leaf spring extend a considerable distance outside of the housing 41. That is the support brackets 35 and 36 will flange outwardly to form a support therefor. This arrangement must be provided for the flat metal leaf spring since a deflection thereof will be noted as the contact is moved from its extreme lower toits extreme upward position by the push rod 18. There will be a tendency for the metal leaf spring 44 to elongate thereby setting up tensional stresses within the leaf spring or guide member 44. These tensional forces can be substantially reduced for a given deflection, by making the length of the leaf spring relatively large with respect to the magnitude of deflection.

In Figure 5 I have shown a modification of the first embodiment of Figures 3 and 4. In the modified view of Figure 5, I have used numerals similar to those used in describing the structure of Figures 3 and 4 for identical components. Thus, the helical biasing spring 32, lodged between the spacers 33 and 34, biases the bridging contact 31 into electrical engagement with the stationary contacts 26 and 28. In the modified view of Figure 5 the guide member is a metal leaf spring which is mounted at only one end thereof, and the opposite end carries the bridging contact 31.

Thus, as seen in Figure 5, the metal leaf spring 54 is mounted at its right end between insulated spacers 55 and 56. Since the modified arrangement of Figure 5 does not require the support brackets 3536 as used in the first embodiment of Figure 3, the insulating spacers 55 and 56 serve the same function as the insulated spacers 52 of Figure 3.

Thus, the metal leaf spring 54 has the bridging contact 31 mounted on the left end thereof by means of the screw 50. The insulator 55 is preferably provided with a cut away section 57 so that the metal leaf spring 54 will not engage a sharp edge as the bridging contact 31 is driven into contact disengagement by the push rod 18. It will be noted that with the modification of Figure 5 that even though the leaf spring 54 is only mounted at one end it nevertheless will prevent both rotation and sliding of the bridging contact 31.

As heretofore noted, since the guide member is a metal leaf spring there will be tension stresses built up therein when same is deflected due to the extreme upward movement of the push rod 18. Thus, it is desirable to have the length of the guide member very much larger than the degree'of deflection of the guide member in order to limit or minimize the magnitude of tensional stresses.

Furthermore, by providing the cantilever mounted arrangement shown in Figure 5 the tensional stresses within the leaf spring 54, have a given deflection and given length, will be considerably less than the tensional stresses which may be built up in a leaf spring which is supported at both ends, such as shown in Figure 3.

In Figure 6 I have shown a second embodiment of my invention wherein the metal leaf spring serves the dual function of both guiding and biasing the bridging contact. In this arrangement, the metal leaf spring must be a relatively strong member, in order to provide sutficient contact pressure between the cooperating contacts.

In the embodiment of Figure 6 the housing is made of an insulating material and extends in the direction indicated in the figure over a considerable length to provide supporting means for the metal leaf spring 64. The housing 60 is provided with openings 61 and 62 to receive the bolts 65 and 66. The bolts and nuts 65 and 66 pass through appropriate openings in the metal leaf spring 64, as seen in Figure 6A, to provide stationary supports for both ends of the leaf spring. The movable bridging contact 31 is secured to the metal leaf spring 64 by means of the nut and bolt 67.

It will be noted that in the second embodiment of Figure 6 and Figure 6A the leaf spring is bowed upwardly when the cooperating contacts are in their engaged position. That is, since the leaf spring provides the biasing pressure for the movable contact it cannot be in either its neutral or lowermost position when the cooperating contacts are engaged. In contra-distinction in the embodiment of both Figures 3 and 5 the leaf spring can be either in its lowermost position or in its neutral position, respectively, since the helical spring 32 provides all of the contact pressure which is required.

However, in the second embodiment of Figure 6 it is necessary to have the metal leaf spring 64 in such a position when the contacts are in engagement that it will impart a sufficient force to the bridging contact 31 to provide ample contact pressure thereto.

As heretofore noted, characteristics for the metal leaf spring 44 of Figure 3 and the metal leaf spring 54 of Figure 5 also exist for the metal leaf spring 64 of Figure 6. That is, the leaf spring will prevent both rotation and sliding of the bridging contact 31 with respect to the stationary contacts 26 and 28.

Hence, in the second embodiment of Figure 6, I have provided a novel arrangement wherein the leaf spring serves the dual function of both guiding the moving contact and biasing same into high pressure contac engagement.

In the foregoing, I have described my invention only in connection with preferred embodiments thereof. Many variations and modifications of the principles of my invention within the scope of the description herein are obvious. Accordingly, I prefer to be bound not by the specific disclosure herein but only by the appending claim.

I claim:

In combination, a stationary contact, a movable contact movable into and out of engagement with said stationary contact, biasing means for biasing said movable contact into contact engagement with said stationary contact, a push rod for operating said movable contact out of engagement with said stationary contact against the action of said biasing means; and means for guiding said movable contact from said disengaged position to said engaged position and preventing both rotation and sliding of said movable contact; said means comprising a metal leaf spring, a housing for said biasing means, said movable contact and said stationary contact; stationary supporting means mounted on said housing and having '7 ends fiariiig a v'i ay theref rom, saiderlds providing station- 359 si1 pp6rts fo'r' the end of said metal leaf spring said spring figidly secured t o said supports; said movable:cef fizictimmintedon said metal 1eaf spring inter- ;ir iedia t eIsaid"siatidna y supports; said spring being subgsiaritiallly fiat between said movable contact and said ls iip p dft.

.Refefences Cited in the file of 'this patent UNITED STATES PATENTS Menzel a June/ 24,,l9,3 0 Ray May 19,;19'42 flube ay- ,1 45, Dreylus -Decfl, 195 3 Kesselririg Degl3, i955 

